Description

ALTER SEQUENCE changes the parameters
of an existing sequence generator. Any parameters not
specifically set in the ALTER SEQUENCE
command retain their prior settings.

You must own the sequence to use ALTER
SEQUENCE. To change a sequence's schema, you must also have
CREATE privilege on the new schema.

Parameters

name

The name (optionally schema-qualified) of a sequence to
be altered.

increment

The clause INCREMENT BY increment is optional. A
positive value will make an ascending sequence, a negative
one a descending sequence. If unspecified, the old
increment value will be maintained.

minvalueNO MINVALUE

The optional clause MINVALUE
minvalue determines
the minimum value a sequence can generate. If NO MINVALUE is specified, the defaults of 1
and -263-1 for ascending and descending
sequences, respectively, will be used. If neither option is
specified, the current minimum value will be
maintained.

maxvalueNO MAXVALUE

The optional clause MAXVALUE
maxvalue determines
the maximum value for the sequence. If NO MAXVALUE is specified, the defaults are
263-1 and -1 for ascending and descending
sequences, respectively, will be used. If neither option is
specified, the current maximum value will be
maintained.

start

The optional clause RESTART WITH
start changes the
current value of the sequence. This is equivalent to
calling the setval function
with is_called = false: the specified value will be returned
by the next call
of nextval.

cache

The clause CACHE cache enables sequence numbers
to be preallocated and stored in memory for faster access.
The minimum value is 1 (only one value can be generated at
a time, i.e., no cache). If unspecified, the old cache
value will be maintained.

CYCLE

The optional CYCLE key word can
be used to enable the sequence to wrap around when the
maxvalue or minvalue has been reached by an
ascending or descending sequence respectively. If the limit
is reached, the next number generated will be the
minvalue or maxvalue, respectively.

NO CYCLE

If the optional NO CYCLE key
word is specified, any calls to nextval after the sequence has reached
its maximum value will return an error. If neither
CYCLE or NO
CYCLE are specified, the old cycle behavior will be
maintained.

OWNED BYtable.columnOWNED BY NONE

The OWNED BY option causes the
sequence to be associated with a specific table column,
such that if that column (or its whole table) is dropped,
the sequence will be automatically dropped as well. If
specified, this association replaces any previously
specified association for the sequence. The specified table
must have the same owner and be in the same schema as the
sequence. Specifying OWNED BY NONE
removes any existing association, making the sequence
"free-standing".

new_name

The new name for the sequence.

new_schema

The new schema for the sequence.

Notes

To avoid blocking of concurrent transactions that obtain
numbers from the same sequence, ALTER
SEQUENCE's effects on the sequence generation parameters are
never rolled back; those changes take effect immediately and are
not reversible. However, the OWNED BY,
RENAME, and SET
SCHEMA clauses cause ordinary catalog updates that can be
rolled back.

ALTER SEQUENCE will not immediately
affect nextval results in backends,
other than the current one, that have preallocated (cached)
sequence values. They will use up all cached values prior to
noticing the changed sequence generation parameters. The current
backend will be affected immediately.

ALTER SEQUENCE does not affect the
currval status for the sequence.
(Before PostgreSQL 8.3, it
sometimes did.)

Some variants of ALTER TABLE can be
used with sequences as well; for example, to rename a sequence it
is also possible to use ALTER TABLE
RENAME.

Examples

Restart a sequence called serial, at
105:

ALTER SEQUENCE serial RESTART WITH 105;

Compatibility

ALTER SEQUENCE conforms to the
SQL standard, except for the
OWNED BY, RENAME, and SET SCHEMA
clauses, which are PostgreSQL
extensions.